1. Field of the Invention
The present invention relates to a package for housing a photosemiconductor element.
2. Description of the Related Art
A conventional package for housing a photosemiconductor element comprises: (a) a substrate made of a ceramics material such as sintered aluminum oxide in general, and having, on the top surface thereof, a recess for housing a photosemiconductor element; (b) a tubular fixing member attached by brazing to a through hole formed on a side of the substrate and the periphery of the substrate around the through hole, having therein a space for transmitting optical signals, and made of metallic material such as an iron-nickel alloy (iron: 50 wt %, nickel: 50 wt %); (c) a light-transmitting member attached to an inside of the tubular fixing member with glass to block the inside; (d) a plurality of wiring conductor layers which is made of tungsten, molybdenum, manganese or the like deposited and led out from the inside of the recess of the substrate to the periphery of the substrate, and to which electrodes of a photosemiconductor element are connected via electrically connecting means such as bonding wires; and (e) a lid attached to the top surface of the substrate to close the recess. A photosemiconductor device is completed as a product by adhering and fixing a photosemiconductor element into the recess of the substrate with an adhesion such as glass, a resin or a brazing material, while electrically connecting the individual electrodes of the photosemiconductor element to the wiring conductor layers via the electrically connecting means such as bonding wires, and thereafter joining he lid to the top surface of the substrate with a sealing material made of glass, a resin, a brazing material or the like to hermetically house the photosemiconductor element into a container composed of the substrate and the lid, while welding and connecting an optical-fiber member to the tubular fixing member by using laser light beams of YAG or the like.
Such a photosemiconductor device causes the photosemiconductor element to excite light in a predetermined manner on the basis of driving signals supplied from an external electric circuit, thereby causing the optical-fiber member to receive the excited light via the light-transmitting member and causing the optical-fiber member to transmit the excited light in a optical fiber thereof, so that the photosemiconductor device is used in high-speed communication and the like.
Further, in the package for housing a photosemiconductor element mentioned above, the tubular fixing member is brazed and attached to the substrate in the following way.
(1) At first, a nickel plating layer and a gold plating layer are deposited in succession on the surface of the tubular fixing member in order to braze and attach the tubular fixing member to the substrate reliably and firmly.
The nickel plating layer is an under member for firmly depositing the gold plating layer on the tubular fixing member, and is deposited on the periphery of the tubular fixing member to a thickness of approximately 0.5 xcexcm to 5 xcexcm by the electrolytic plating method or the electroless plating method.
Further, the gold plating layer has the function of enhancing the wettability of a brazing material to the tubular fixing member, and is deposited on the nickel plating layer to a thickness of approximately 1 xcexcm to 3 xcexcm by the electrolytic plating method or the electroless plating method.
(2) Next, the light-transmitting member is attached to an inside of the tubular fixing member with glass to block the inside.
The light-transmitting member is attached to the tubular fixing member by applying, for example, low-melting-point solder glass having a melting point lower than that of the light-transmitting member, to the inside of the tubular fixing member, placing the light-transmitting member on the coating low-melting-point solder glass, and thereafter heating them up to a temperature of approximately 450xc2x0 C. in the air to melt the low-melting-point solder glass.
(3) Finally, the tubular fixing member is brazed and attached to the periphery of the substrate around the through hole with a low-melting-point brazing material comprising an gold-tin alloy or the like, whereby a package for housing a photosemiconductor element is completed as a product.
The tubular fixing member is brazed to the substrate by placing the tubular fixing member on the periphery of the substrate around the through hole so as to sandwich the low-melting-point brazing material made of a gold-tin alloy (gold: 80 wt %, tin: 20 wt %) or the like, and thereafter heating them up to a temperature of approximately 300xc2x0 C. to melt the low-melting-point brazing material.
However, this conventional method for producing a package for housing a photosemiconductor element has a drawback of being incapable of firmly brazing and attaching the tubular fixing member to the substrate, because when the light-transmitting member is attached to the inside of the tubular fixing member with glass, part of the nickel plating layer deposited on the periphery of the tubular fixing member is, due to heat and atmosphere in glass attachment, diffused in the gold plating layer and exposed to the surface of the gold plating layer, which is oxidized to become a large amount of nickel oxide on the surface of the gold plating layer, with the result that the poor wettability of the nickel oxide to the brazing material largely decreases the joint strength of the brazing material to the tubular fixing member.
Then, in order to overcome the drawback described above, it may be considered to deposit the nickel plating layer and the gold plating layer in succession on the surface of the tubular fixing member after attaching the light-transmitting member to the inside of the tubular fixing member with glass.
However, this may induce another drawback. The glass attaching the light-transmitting member to the inside of the tubular fixing member is low-melting-point solder glass, and the low-melting-point solder glass has poor chemical resistance. Therefore, in the case of depositing the nickel plating layer and the gold plating layer on the surface of the tubular fixing member after attaching the light-transmitting member to the inside of the tubular fixing member with the glass, the glass is melted by a chemical of a plating solution, with the result that the light-transmitting member is detached from the tubular fixing member.
The present invention, which has been made in view of the drawbacks described above, is aimed at providing a method for producing a package for housing a photosemiconductor element made to have a considerably high reliability by firmly brazing and attaching a tubular fixing member to a substrate.
The invention provides a method for producing a package for housing a photosemiconductor element,
the package for housing a photosemiconductor element comprising a substrate having a recess for housing the photosemiconductor element on a top surface of the substrate, a through hole being formed in a side of the substrate; a tubular metallic fixing member which is brazed to an outer surface of the substrate around the through hole, an optical fiber member being connected to one end of the tubular metallic fixing member; a light-transmitting member attached to an inside of the tubular metallic fixing member to block the inside; and a lid attached to the top surface of the substrate to close the recess,
the method comprising:
(a) a first step of depositing a nickel plating layer on a surface of the tubular metallic fixing member and successively depositing a gold plating layer thereon without occurrence of diffusion of the nickel plating layer to the gold plating layer, and attaching the light-transmitting member to an inside of the metallic fixing member with glass without occurrence of damage to a surface of the light-transmitting member; and
(b) a second step of brazing and attaching the metallic fixing member to the outer surface of the substrate around the through hole with a brazing material.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the first step comprises:
(a1) a step of depositing a nickel plating layer on a surface of the tubular metallic fixing member and successively depositing a gold plating layer thereon;
(b1) a step of attaching the light-transmitting member to an inside of the metallic fixing member with glass; and
(c1) a step of removing part of a surface of the gold plating layer deposited on the nickel plating layer on the surface of the metallic fixing member, by an etching treatment.
According to the method for producing a package for housing a photosemiconductor element of the invention, after the light-transmitting member is attached to the metallic fixing member with glass, part of the surface of the gold plating layer deposited on the nickel plating layer on the surface of the metallic fixing member is removed by an etching treatment. Therefore, when a large amount of nickel oxide having a poor wettability to a brazing material is formed, due to diffusion and oxidation of the nickel plating layer serving as an under member, on the surface of the gold plating layer, the nickel oxide is removed by an etching treatment, with the result that the joint strength of the brazing material to the tubular metallic fixing member is largely enhanced, and the tubular metallic fixing member can be considerably firmly brazed and attached to the substrate.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that a thickness d12 of the nickel plating layer is approximately 0.5 to 5 xcexcm, a thickness d13 of the gold plating layer is approximately 3 to 8 xcexcm, a thickness d23 of the part of the surface of the gold plating layer, subjected to the etching treatment is approximately 0.5-3 xcexcm.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that an etchant of the etching treatment comprises potassium cyanide, lead monoxide and chelating agent.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the first step comprises:
(a2) a step of depositing a nickel plating layer on a surface of the tubular metallic fixing member, and subjecting the nickel plating layer deposited on the surface of the tubular metallic fixing member, to a heat treatment in a reducing atmosphere;
(b2) a step of depositing a gold plating layer on the nickel plating layer; and
(c2) a step of attaching the light-transmitting member to an inside of the metallic fixing member with glass.
According to the method for producing a package for housing a photosemiconductor element of the invention, the nickel plating layer deposited on the surface of the metallic fixing member is subjected to a heat treatment in a reducing atmosphere, and the nickel plating layer is printed on the metallic fixing member. Therefore, it would hardly occur that when the light-transmitting member is attached to the inside of the metallic fixing member with glass, part of the nickel plating layer deposited on the surface of the metallic fixing member is diffused in the gold plating layer due to heat and atmosphere in glass attachment and exposed to the surface of the gold plating layer, with the result that it would not happen that a large amount of nickel oxide is formed on the surface of the gold plating layer. Therefore, the wettability of the gold plating layer to the brazing material may become so excellent that the joint strength of the brazing material to the metallic fixing member is largely enhanced, whereby the metallic fixing member can be considerably firmly brazed and attached to the substrate.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the first step comprises:
(a3) a step of depositing a nickel plating layer comprising 1-65 wt % cobalt and 35-99 wt % nickel on a surface of the tubular metallic fixing member and successively depositing a gold plating layer thereon; and
(b3) a step of attaching the light-transmitting member to an inside of the metallic fixing member with glass.
According to the method for producing a package for housing a photosemiconductor element of the invention, the nickel plating layer deposited on the surface of the metallic fixing member comprises 1-65 wt % cobalt. Therefore, when the light-transmitting member is attached to the inside of the metallic fixing member with glass, the cobalt effectively prevents part of the nickel plating layer deposited on the surface of the metallic fixing member from diffusing into the gold plating layer due to heat and atmosphere in attaching the light-transmitting member with glass, and the nickel plating layer does not appear on the surface of the gold plating layer at all. Accordingly it would not occur that a large amount of nickel oxide is formed on the surface of the gold plating layer. Therefore, the wettability of the gold plating layer to the brazing material may become high at all times to largely enhance the joint strength of the brazing material to the metallic fixing member, so that the metallic fixing member can be considerably firmly brazed and attached to the substrate.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the first step comprises:
(a4) a step of depositing a nickel plating layer on a surface of the tubular metallic fixing member and successively depositing a gold plating layer thereon;
(b4) a step of attaching the light-transmitting member to an inside of the metallic fixing member with glass; and
(c4) a step of subjecting the metallic fixing member to a heat treatment in a reducing atmosphere.
According to the method for producing a package for housing a photosemiconductor element of the invention, after the light-transmitting member is attached to the metallic fixing member with glass, the metallic fixing member is subjected to a heat treatment in a reducing atmosphere. Therefore, when a large amount of nickel oxide having a poor wettability to the brazing material is formed on the surface of the gold plating layer due to diffusion and oxidation of the nickel plating layer serving as an under member, the nickel oxide is thoroughly removed by the heating treatment in the reducing atmosphere, with the result that the joint strength of the brazing material to the tubular metallic fixing member is largely enhanced, so that the tubular metallic fixing member can be considerably firmly brazed and attached to the substrate.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the reducing atmosphere is one selected from the group consisting of hydrogen atmosphere nitrogen atmosphere and an atmosphere of a mixture of hydrogen and nitrogen.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the heat treatment in the reducing atmosphere is carried out at temperatures of 500-1100xc2x0 C.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the heat treatment in the reducing atmosphere is carried out at temperatures (e.g. 200-420xc2x0 C.) lower than a melting point of the glass for use in attachment of the light-transmitting member.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the first step comprises:
(a5) a step of attaching the light-transmitting member to an inside of the metallic fixing member with glass;
(b5) a step of coating an exposed surface of the glass with a protective film; and
(c5) a step of depositing a nickel plating layer on an exposed surface of the tubular metallic fixing member and successively depositing a gold plating layer thereon.
According to the method for producing a package for housing a photosemiconductor element of the invention, an exposed surface of the glass with which the light-transmitting member is attached to the inside of the metallic fixing member is coated with a protective film. Therefore, when the nickel plating layer and the gold plating layer are deposited in succession on the surface of the metallic fixing member to which the light-transmitting member is attached with glass, the glass would not be melted by a plating solution because protected by the protective film. Moreover, after the light-transmitting member is attached to the inside of the metallic fixing member, the nickel plating layer and the gold plating layer are deposited on the surface of the metallic fixing member. Therefore, it would not occur that part of the nickel plating layer is diffused and exposed to the surface of the gold plating layer and thereby oxidized to become nickel oxide, with the result that the attachment strength of the light-transmitting member to the metallic fixing member is enhanced, and the wettability of the gold plating layer to the brazing material may become high, so that the tubular metallic fixing member to which the light-transmitting member is attached can be considerably firmly brazed and attached to the substrate.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the protective film is one or more selected from the group consisting of silicon oxide, magnesium fluoride and titanium oxide, and
the protective film is deposited on an exposed surface of the glass by a vacuum deposition method or ion beam method.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the first step comprises:
(a6) a step of depositing a nickel plating layer on a surface of the tubular metallic fixing member and successively depositing a gold plating layer thereon; and
(b6) a step of attaching the light-transmitting member to an inside of the metallic fixing member with glass having a melting point of 320-400xc2x0 C.
According to the method for producing a package for housing a photosemiconductor element of the invention, the glass attaching the light-transmitting member to the inside of the metallic fixing member has such a low-melting-point as 320-400xc2x0 C. Therefore, when the light-transmitting member is attached to the metallic fixing member with the glass, it would not happen that part of the nickel plating layer deposited on the surface of the metallic fixing member is diffused in the gold plating layer, with the result that it would not happen that part of the nickel plating layer is diffused and exposed to the surface of the gold plating layer ad thereby oxidized to become nickel oxide. Therefore, the wettability of the gold plating layer to the brazing material may become preferable to largely enhance the joint strength of the brazing material to the tubular metallic fixing member, sot hat the tubular metallic fixing member can be considerably firmly brazed and attached to the substrate.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the glass with which the light-transmitting member is attached to the inside of the metallic fixing member has a low-melting-point (e.g. approx. 450=20  C.) lower than that of the light-transmitting member.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the low-melting-point glass comprises 50-65 wt % lead oxide, 0-10 wt % silicon oxide, 5-8 wt % boron oxide, 0-7 wt % aluminum oxide, 0-20 wt % tin oxide, 2-15 wt % titanium oxide and 10-15 wt % lead fluoride, and has a melting point of 320-400xc2x0 C.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that a thickness d23 of the gold plating layer is approximately 1-3 xcexcm.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the substrate is made of ceramics or metal, and the metallic fixing member is made of a gold-nickel-cobalt alloy or iron-nickel alloy.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that the light-transmitting member is made of noncrystalline glass.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that a metallic flange to which the optical fiber member is fixed, is fixed to the metallic fixing member by laser welding.
In the method for producing a package for housing a photosemiconductor element of the invention it is preferable that a thickness d12 of the nickel plating layer is approximately 0.5‥5 xcexcm.
The invention provides a low-melting-point glass comprising 50-65 wt % lead oxide, 0-10 wt % silicon oxide, 5-8 wt % boron oxide, 0-7 wt % aluminum oxide, 0-20 wt % tin oxide, 2-15 wt % titanium oxide and 10-15 wt % lead fluoride, and has a melting point of 320-400xc2x0 C.